ASH, K9 and Sarah Jane Smith! Happy overload!
Their tiny videos don't do the visuals justice.
I have a great screencap on my flickr account.
I just wish he was a multi-episode character...
You can also join in the Doctor Who fun at whedonesque.org if you're a fan...

ps. Sarah Jane last appeared THIRTY years ago on Doctor Who
Elisabeth Sladen (the actress) looks freakin fantastic!

pps. Last week's episode is a great warmup for this one (Tooth and Claw)
and most any Buffy fan should enjoy it, even if you haven't watched Who before...

Zip-Ity, the reality is there is a TON of legacy Doctor Who. It would take you years to watch it if you only watched a few episodes per week. It's very possible to enjoy the new Doctor Who without seeing the old but there will always be little stuff (like K9) that is being put in as a fan-service for those that did watch all the old.

Makes me wonder sometimes if there will one day be a "Buffy 2025" or something like that which references the little stuff we loved so much. Or maybe one of Joss's kids will make "Fray" when they get older :-)

Zip-ity-Do-Da, Doctor Who is the longest running sci-fi series ever and so as TaraLivesOn says there's a lot of history there (something like 720 episodes - though the older ones were only half an hour long) so you could spend a lot of time catching up.

If you wanted to check out some old ones i'd probably recommend some Tom Baker episodes (e.g. 'Genesis of the Daleks' or 'Talons of Weng Chang') or possibly one of the specials like 'The Five Doctors' to give you a feel for the Doctor's previous incarnations. Be warned though, BBC 'special' effects weren't anywhere near as special back then so you have to kind of squint past the wobbly sets and dodgy 'laser' beams and just enjoy the fun scripts and gloriously eccentric performances (especially Tom Baker's - man's a legend ;).

Zeppo, you might actually want to watch the first (new) season on scifi channel or rent the season one DVD's? Jumping into season two might be impossibly confusing. Imagine trying to jump into the second episode of season four Buffy and figure out what's going on - it could be done but you wouldn't really "get it".

TheZeppo, you could try The Sun tomorrow. As much of a scummy waste of paper as it is, tomorrow will feature a voucher where you can redeem "Rose" (the first epsiode of the first new series) which explains the show again for new viewers. They can be redeemed at Somerfield, Martins, Mccoll's, Fourboys or Dillons